1. Field of the Invention
The present invention relates to disk drives, and in particular to an actuator arm which isolates vibration emanating from a voice coil motor on the actuator arm.
2. Description of Related Art
Conventional disk drives for use in workstations, personal computers and portable computers are required to provide a large amount of data storage within a minimum physical space. In general, Winchester type disk drives operate by transferring data between read/write transducing heads and one or more rotating magnetic storage disks. Positioning of the heads at the desired location of a respective data track on the disk is accomplished by an actuator assembly coupled to control electronics. The electronics control rotation of the disk, positioning of the actuator assembly, and the read/write functions of the head.
Greater demands are being placed on disk drives because they are key components to the high performance computer systems of today and the future. With the ongoing significant increase in real-time usage of high-resolution, digitized graphical and video images in desktop computers, the development of portable information appliances for both home and office environments, and emerging fiber-optic and satellite-linked Internet international communication infrastructure, it is of paramount importance to have available recording devices which offer higher performance and precision for the massive online computer data storage applications of the future. All such systems require a hard drive having high capacity storage capability. One way to increase storage capacity is to decrease the read/write head "flying height" (i.e. the height the head flies above the disk during drive operation). However, at present day flying heights, intermittent contact of the read/write head with the disk becomes a significant design factor. In conventional disk drive Systems, such intermittent contact may result in read/write errors and/or disk drive failure, and may result from mechanical resonances, spindle runouts, temperature drifts, humidity variations, external shocks and vibrations, bearing hysteresis, cable bias and various other sources.
Since disk drives will most likely remain the primary memory device in computer applications, disk drives will require greater storage capacities, while at the same time becoming more compact, faster, and less expensive. These changes will require greater emphasis on lower flying heights for heads, higher data transmission speeds, and more cost-effective disk drive assemblies. One factor which must be addressed in meeting these demands is the vibration resonance of the actuator assembly. The actuator assembly is responsible for accurately positioning the read/write head over the desired track for retrieving or storing information. Because the actuator assembly is an essential part of the high speed data transmission path, there is a need for an improved actuator arm which reduces or eliminates mechanical vibrations. These vibrations occur as a result of the voice coil forces exerted on the actuator arm by the voice coil motor. Often times in conventional disk drives, vibrations originating from sources within the disk drive are transmitted to neighboring structures, to the detriment of the internal environment.
The actuator assembly consists of a voice coil motor assembly, an actuator arm, a suspension assembly, and read/write heads. The actuator arm is attached to the suspension assembly which holds the read/write heads in position while pressing the heads toward the disk surface. The head flies above the disk at a height established by the equilibrium of the suspension force and the force of the air stream under the head as the disk rotates. The voice coil motor assembly comprises a voice coil mounted at a back end of the actuator arm, between two magnets attached to a top and bottom plate and secured by posts. Upon introduction of a current through the voice coil, the magnets exert a force on the voice coil to pivot the actuator assembly and move the read/write heads over a desired data track. In addition to the positioning function, the voice coil maintains the read/write head position relative to the desired track being read, constantly making fine-scale position corrections and adjustments to follow that particular track.
Time-varying forces exerted on the voice coil by the magnets create vibration. The material of a standard metal actuator arm has a very small vibration damping coefficient, and therefore, any vibration caused by the voice coil motor will resonate through the actuator arm. This mechanical vibration is transmitted during normal drive operation through the actuator arm to the head suspensions and ultimately to the read/write heads themselves.
Any vibration generated by the voice coil will affect the flying height, as well as the positioning of the read/write heads. In order to maintain proper head/media interface, the actuator assembly must be very flexible. Specifically, components of the suspension assembly are designed to be flexible (while other parts of the actuator assembly are designed to be rigid, such as the actuator arm) because compliance in the components allow the read/write head to be retained close to the disk under severe vibration or shock conditions. However, mechanical flexibilities in the actuator assembly tend to increase vibration in the actuator assembly because the actuator components have one or more resonant frequencies. Reduction of the vibration amplitude of the read/write heads under operating conditions will allow a higher track density and thus a higher disk information storage capacity.
Vibration in the actuator further impairs settling of the actuator assembly to a position aligned over a desired data track, thereby adversely affecting access times. Access time is the interval between the time a request is made by the control system and the time the data is available from the disk drive, and is a combination of seek time, head switch time and rotational latency. Specifically, it is a measure of how long it takes to position a read/write head over a particular track and find the desired sector or sectors within the track for reading or writing. Under moderate vibration, the read/write head will not settle quickly to its proper position above the desired data track. As a result, the access time will be extended because the read/write head must wait for another entire disk rotation before data can be transferred. Under severe vibration, the head may never settle over the desired track. In this case, the control system will sense a fault and shut the disk drive down. At present track densities, a lateral vibration of the read/write head on the magnitude of even ten millionths of an inch relative to a data track center line on a disk will cause the processes of reading information from the disk or writing information to the disk to be aborted. It is therefore crucial for actuator arm designers to seek the optimal combination of compliancy in the yaw, pitch and roll torques, while producing the greatest stability and immunity to vibrations in order that the access time is not severely affected or the disk drive shut down. Given the tolerances involved in manufacturing disk drives and the speed at which drives operate, the ability to locate data and move the heads accurately to read or write data is essential to increased data transmission speeds.
To counter the effects of vibration and ensure precise head alignment and positioning, conventional disk drives have incorporated an electromechanical technique called servo positioning which compensates for vibration created by the actuator assembly. The servo positioning device provides feedback to the drive electronics which control the position of the read/write heads (the servo-positioning device is integrated into the read/write head). When the read/write heads arrive at an intended track location, the read/write heads read positioning information embedded in a servo data location. The read/write heads send back the information to the servo-positioning device. The drive electronics then adjust the position of the actuator arm to accurately center the read/write head over the desired track so that a maximum signal may be read from the embedded information. However, this method can be difficult to implement in some disk drives, such as disk drives which use multiple zone recording techniques. Also, at certain frequencies where the actuator arm exhibits severe vibrations, the servo control positioning device may be severely taxed.
Another device used for countering the effects of vibration caused by the actuator assembly is a constrained layer damper which is applied on the flexure of the suspension assembly. The damper device is made of, for example, a Mylar material which has an adhesive attached to it. Together the Mylar and adhesive have intrinsic damping properties and reduces minor vibration. The damper device dissipates some of the vibration energy of the actuator assembly through applying friction However, this method can be expensive by adding fabrication costs to the disk drive, and can be difficult to install properly.